1. Field of the Invention
The present invention relates to a magneto-optical recording layer and a magneto-optical disk adopting the same, and more particularly, to a magneto-optical recording layer with a double-layer structure having a first magnetic layer made of an amorphous alloy of a light rare earth-transition metal and a semi-metal (metalloid), and a second magnetic layer made of an amorphous alloy of a heavy rare earth-transition metal, and a magneto-optical disk adopting the same.
A magneto-optical disk has a higher information memory density as compared with that of a conventional magnetic disk, and a random access characteristic by which desired information is easily searched. Thus, the magneto-optical disk has lately attracted considerable attention as a high density recording medium which can substitute for a hard disk or a magnetic tape.
2. Description of the Related Art
In a conventional method, the recording layer of a magneto-optical disk is manufactured by sputtering or vapor-depositing a binary alloy of a rare earth-transition metal (RE-TM) having a perpendicular magnetic easy axis on the surface thereof.
The coercive force and magneto-optical effect of terbium iron (TbFe) or terbium cobalt (TbCo) as the binary RE-TM alloy are strong enough, but the corrosion resistance thereof is weak.
To overcome the above problems, an alloy of one of the above-mentioned binary alloys and another metal has been used as a material for the magneto-optical recording layer.
There has been developed an amorphous alloy of terbium iron cobalt (TbFeCo) obtained by adding Co to TbFe, which is excellent for information storage stability and is suitably used for long wavelength laser beams (700.about.1,000 nm). Thus, if an amorphous alloy is used in a short wavelength region (about 400 nm) to increase recording density of information, photoelectric energy is decreased, thereby reducing a Kerr rotation angle. The decreased Kerr rotation angle lowers a carrier-to-noise ratio (CNR) which exhibits reproduction characteristics of the magneto-optical recording medium. Thus, the amorphous alloy of TbFeCo is not suitable as the material for the recording layer of a short wavelength recording medium for the high density recording.
To solve the above problems, an alloy of a light rare earth metal-transition metal (LRE-TM), which increases the Kerr rotation angle in the short wavelength region, has attracted public attention as a material for the recording layer of a short wavelength magneto-optical recording medium. However, since an alloy of NdFeCo is ferro-magnetically coupled, the demagnetizing energy thereof is high. Thus, the alloy of NdFeCo does not have magnetic anisotropy perpendicular to the recording layer plane, so that the alloy cannot be used as the material for the recording layer of short wavelength magneto-optical recording media.
To solve this problem, the light rare earth metal has been partially substituted with a heavy rare earth metal. That is, the ferro-magnetic coupling is partially substituted by a ferri-magnetic coupling to decrease demagnetizing energy, thereby resulting in the development of an alloy which is capable of inducing perpendicular magnetic anisotropy. However, in this case, the Kerr rotation angle is reduced in the short wavelength region as much as the magnetic moment of the light rare earth metal substituted by the heavy rare earth metal.